Prior to the present invention, various methods were available to make silicone foam which is used as a thermal and electrical insulator, a flame barrier, or in cushioning applications. Although elastomeric silicone foams have excellent physical properties, their use has been somewhat restricted since these materials are generally more expensive than the corresponding organic foams. In an effort to overcome the cost disadvantages of silicone foams over organic foams, silicone foam manufacturers are constantly developing techniques for reducing the density of the silicone foam while trying to maintain the strength of the fabricated structure. One method of reducing silicone foam density, while maintaining strength is shown by Modic, U.S. Pat. No. 4,418,157. Other procedures are constantly being developed to further reduce the cost advantages of silicone foams with respect to organic foams.
The present invention is based on the discovery that a silicone foam having reduced foam density can, nevertheless, be made with a satisfactory degree of tensile strength by incorporating into the foamable mixture an effective amount of a silicone polyimide where the silicone block in the silicone polyimide has chemically combined methylvinyl siloxy units.